The internal combustion engines used in automotive engineering have a drive shaft by way of which the energy produced during the combustion is transferred in the form of a torque to the drive train of the motor vehicle to be driven. In the case of reciprocating piston engines this drive shaft is referred to as the crankshaft. As a basic principle the drive shaft is mounted in such a manner that it is capable of rotating in two opposite directions of rotation. However, many important components of the internal combustion engine are calibrated only for one direction of rotation of the drive shaft, referred to in the following as forward direction of rotation. Thus for example the entire intake tract, the components and sensors contained therein, are designed only to guarantee the fresh air supply of the internal combustion engine. Similarly, for example, the exhaust tract of the internal combustion engine is designed only for discharging the hot combustion exhaust gases from the combustion chambers into the surrounding area. The same also applies for example to the control of the inlet and outlet valves, the opening times of which are designed only for operation in the forward direction of rotation. Furthermore, most modern internal combustion engines have an electronic control device which controls the fresh-air mass flow, the ignition and the fuel injection on the basis of the output signals from the sensors. The control functions implemented in the control device guarantee the correct interaction of all actuators, but only for the case where the drive shaft rotates in the forward direction of rotation. There are however driving situations in which a reverse rotation of the drive shaft is possible, for example if the motor vehicle is rolling backwards with the drive train closed (gear selected) on a steep slope. If the reverse rotation of the drive shaft is not detected, considerable damage to the internal combustion engine can occur as a result of the fuel injection and the ignition being started.
Hitherto, detection of the reverse rotation of the drive shaft has only been possible by means of a specially designed and costly sensor. With the aim of reducing the production costs of motor vehicles, the motor vehicle manufacturers endeavor to further reduce the number of sensors.